I just set-up my rig last night.

All cards are brand new.
All drivers have been updated. (Using GeForce experience.)

Motherboard: ASRock H81 Pro BTC R2.0 (UEFI driver 1.20)
OS: Windows 10 Pro
Graphics Cards: 4x GTX 1060 6GB (3 MSI Gaming X // 1 Inno3D Gaming OC)

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After finally being able to get the 4th GPU (The Inno3D Gaming OC GTX 1060) to appear in Device Manager, it appears but has a little yellow exclamation mark on it.

I click on 'Update Driver', 'Search automatically for updated driver software' and it says "The best drivers for the device are already installed."

In the device status, it says: "Windows has stopped the device because it has reported problems. (Code 43.)"
In the resources, it says: "The device isn't using any resources because it has a problem."